The present disclosure relates generally to semiconductor device manufacturing, and more particularly to a method and system for repairing photolithography mask reticles used in the component and circuit patterning processes of a semiconductor device substrate.
The manufacture of semiconductor integrated circuits (ICs) and devices require the use of many photolithography process steps to define and create specific circuit components and circuit layouts onto an underlying substrate. Conventional photolithography systems project specific circuit and/or component images, defined by a mask pattern reticle, onto a flat substrate coated with a light sensitive film (photoresist) coating. After image exposure, the film is then developed leaving the printed image of the circuit and/or component on the substrate. The imaged substrate is subsequently processed with techniques such as etching and doping to alter the substrate with the transferred pattern.
It is critical to the yields of the photolithography operations and to the product yields that the mask reticles are free of defects and damage that may be transferred as undesired patterns and images upon the product substrate.
Advanced semiconductor manufacturing operations utilize mask reticle defect inspection systems to help identify and measure the mask reticle defects and damage. In addition, mask reticle repair systems incorporating focused ion beams (FIBs), are usually used to repair the mask reticles such that the reticles can again, become usable for production operations. The use of these mask reticle inspection and repair systems upon new and in-production mask reticles save the manufacturing operations significant costs related to poor process and device yields, as well as costs related to having new mask reticles fabricated and qualified for production usage.
Mask reticle defects manifest largely by two major forms. Transparent defects are light-passing defects that are located upon regions of the mask reticles where opaque material should be located. The conventional repair method for transparent defects is via the use of a programmed FIB, usually a carbon-rich or metallic ion beam of low keV energy, to deposit an adherent opaque film onto the identified repair regions of the mask reticle. Opaque defects are light-blocking defects that are located upon regions of the mask reticles where such material should be absent. The conventional repair method for opaque defects is via the use of a programmed FIB, usually a Gallium ion beam of between 30 to 75 kilo-electron volts (keV) energy, to etch or sputter the identified defect off of the mask reticle.
Ideally, opaque defect removal must be performed with some precision as to not over-etch and induce new damage to the mask substrate material (typically quartz) located under the removed defect. Such mask substrate damage may itself, be manifested as a new mask reticle defects and damage that may be transferred as undesired patterns and images upon the product substrate. The FIB etching dosage (or etch quantity) must be sufficient enough to clear and remove the entire height and volume of the opaque defect region without inducing significant damage to the underlying mask substrate. Many semiconductor manufacturing operations may choose to maintain a relatively high, fixed FIB etching dosage to ensure complete removal of the opaque defects. The conventional method counts upon a net benefit gain from the removal of the opaque defect versus the possible creation of new mask defects.
Other semiconductor manufacturing operations choose to implement extra procedures to more precisely remove the opaque defects without inducing additional mask reticle defects. Additional procedures are implemented to measure the height of the opaque mask reticle defects in order for a precise FIB etch dose to be determined to remove the defect without damage to the mask substrate. Typical techniques used to measure height of the opaque defects include atomic force microscopy (AFM) and scanning electron microscopy (SEM). Such analytical techniques are capable of obtaining defect height measurements with the required nano-meter scale precision and accuracy.
However, such analytical procedures are not well-suited for an efficient manufacturing operation. These analytical tools and procedures require highly-trained operational expertise, typically an engineer or specialized technician instead of the standard manufacturing operator level expertise. These analytical tools themselves are expensive and slow to operate, requiring much dedicated capital expense as well as much focus and time to perform the required procedures. These translate to high costs associated for the measurement operations and for the time-related costs due to loss of production usage of the measured mask reticle.
What is desirable is an improved opaque defect removal method that can precisely remove the undesired defect without inducing any additional damage upon the mask reticle. The improved method is also desired to be easily incorporated into the manufacturing operations with minimal requirements for engineer and special expertise. Such method would also be of low operational costs as well as incurring minimal impact to the non-production service period of the mask reticles in the repair cycle.